Menkes disease is an X-linked recessive disorder of copper transport caused by defects in a gene that encodes an evolutionarily conserved copper-transporting ATPase. In mammals, this gene product functions as an intracellular pump to transport copper into trans-Golgi spaces for incorporation into copper-requiring enzymes, and also mediates copper exodus from cells. The disorder presents in infancy with delayed development, failure to thrive, neurodegeneration, and premature death (typically by 3 years of age). Our work on this disorder includes development of rapid and reliable neurochemical and molecular techniques for very early diagnosis, efforts which dovetail with a clinical trial of very early copper histidine treatment for affected infants. We use cell biological, molecular, and biochemical approaches to characterize enrolled patients and to correlate with neurodevelopmental outcomes. Confocal imaging of patient fibroblasts is used to assess quantity and localization of mutant Menkes gene products. The blood-brain barrier poses a challenging treatment obstacle in many Menkes disease patients, and we hypothesized a molecular basis for treatment responsivity in the minority of patients (about 1 in 5) who respond successfully (normal neurodevelopmental outcomes) to early copper histidine. These patients have mutations that enable at least some residual copper transport to the developing brain. Consequently, we are developing alternative therapeutic approaches, including intracerebroventricular copper administration, that bypass the blood-brain barrier. To assess safety and determine a maximum tolerated dose (MTD) of copper histidine, we began an animal protocol of intracerebroventricular copper histidine administration in adult male rats and established a maximum tolerated dose of 0.5 ?g. These studies found no statistically significant differences in behavior, growth or brain histopathology between animals receiving the MTD of copper histidine and saline-treated controls. These findings are relevant to determining a suitable intracerebroventricular dose for human administration in selected Menkes disease patients.